-Mr. Norman Wiard, tho inventor oí the Wiard gnu, proposed as a thoory tho expansiou of the metal of tho boiler, oaus'.■(] by super hented steam aoting on n portion of thesuríaoe. The boiler abovo the water-line is thus greatly heBtecl, and thns more expatided than the metal in contint with the water. The boiler is thus strained and weakoued, so that it may yield to the ordinary pressure of the steam. Tlio explosión rarely or uever takes place while tho origine is werking, hut when it is Bturted íifter a short rest. Tho stoppíigí of the entine often canses au unequnl heitirig and exponsion of th boilur, which it is un:iblo to bear. He said that the exptosive f;rce of the stoíiin was Cüused by tho iriotiiBti tutu coiitnunieated to aid it when tho rupturo takes phico. ti mm l Irj Jack Frost has been plajing very ïharji tli'm week.